Gender

Looking at this topic has just caused a paleotology class flashback.I don't have specific information, but I recall studying forams that had two distinct morphologies (within a species). One form was a result of asexual reproduction, the other was a result of sexual reproduction.I don't recall if these were extinct or modern species.Moose------------------
BS degree, geology, '83
Professor, geology, Whatsamatta U
Old Earth evolution - Yes
Godly creation - Maybe

quote:

---

Originally posted by minnemooseus:
Looking at this topic has just caused a paleotology class flashback.

​

I don't have specific information, but I recall studying forams that had two distinct morphologies (within a species). One form was a result of asexual reproduction, the other was a result of sexual reproduction.

​

I don't recall if these were extinct or modern species.

​

Moose

​

---

Moose,There are a few examples, but ferns are one. They have an asexual stage, & a sexual one. The plants exist as two separate, different stages, completely different in appearance. Aphids can reproduce asexually, as well. I'm sure there are many more. Single celled eukaryotes do it all the time, sporazoans (malaria etc) for example have asexual & sexual stages.In short, there is no reason why asexual reproduction continued undisturbed in eukaryotic single cells, whilst a sexual stage developed alongside it.Also, sexual reproduction as a method of replication was complete at the single celled stage before it was extrapolated into multicellular organisms. I mean by that, that there was no such thing as an "asexual dinosaur" that decided to develop sexual organs.Even some prokaryotes are able to form colonies, in which asexual reproduction is undertaken by "asex" cells. ie. Specific reproductive cells.Mark------------------
Occam's razor is not for shaving with.

Cobra Snake, why don't you try keeping up with the literature in the field? Gould and Dawkins (neither of them exactly obscure writers) have both written on this subject - not only why sexual reproduction is advantageous, but how it might have evolved. Perhaps you would be better served actually researching topics, rather than posting snide "or doesn't any scientist know?" remarks that only illustrate your ignorance of the issue.

[QUOTE]Originally posted by mark24:
[b]There are a few examples, but ferns are one. They have an asexual stage, & a sexual one. The plants exist as two separate, different stages, completely different in appearance.[/QUOTE][/b]Technically all plants have "phases" like that, the flowering parts being labeled as the sexual stage of the lifecycle. But I don't read that as too interesting considering that the sexual stage of the lifecycle is attached to the sporophyte stage. Mosses have basically the same problem.Ferns are great examples because they're not attached.

​

[This message has been edited by gene90, 02-06-2002]

if this were true than couldnt any single celled organism have a large chance of becoming a multicelled two sexed organism?------------------
"Overspecialize and you breed in weakness" -"Major" Motoko Kusanagi

quote:

---

Originally posted by toff:
Cobra Snake, why don't you try keeping up with the literature in the field? Gould and Dawkins (neither of them exactly obscure writers) have both written on this subject - not only why sexual reproduction is advantageous, but how it might have evolved. Perhaps you would be better served actually researching topics, rather than posting snide "or doesn't any scientist know?" remarks that only illustrate your ignorance of the issue.

---

First of all, I would like to apologize for asking a question related to the creation/evolution debate. Clearly I was irresponsible in my blatant act of asking a question in a debate forum. Furthermore, I would like to ask your forgiveness for wondering if any scientist has a plausible theory regarding the evolution of sex. I would also like to ask if you could direct me to any literature involving sex written by Gould/Dawkins. I would also like to know if you could provide your own examples of why it is plausible. Given your extreme IQ, you should have no problem thoroughly explaining the phenomenon yourself.But most of all, I beg your forgiveness for questioning the well-researched (and clearly infallible) evolutionary theory. I should have no right to challenge such orthodoxy in a debate forum.Sorry for any inconvienience I have cause you.

Cobra_snake has somehow overlooked message 15.

[QUOTE]Originally posted by gene90:
[b] Please clarify what you mean by "mutations...at one time". [/QUOTE]What I mean, is how many mutations would have to occur in both the male and female of the species to allow sexual reproduction. However, I'm sure you know of a simpler way in which sexuality could of occured without requiring these miracles (no sarcasticness intended on this comment). If you believe that sex could develop in a simpler way, could you please show me? It seems that no matter what, a long string of mutations would have to occur, even for the simplest gender difference in a species. Thanks.

[QUOTE][b]What I mean, is how many mutations would have to occur in both the male and female of the species to allow sexual reproduction. [/QUOTE][/b]A lot to get to where we are today, but probably not that many for the paths of male and female organisms in a population to begin to diverge. I can speculate about that but since this probably happened in the protists hundreds of millions of years ago, there is no fossil evidence I'm aware of. The question is whether that many mutations could have occured through the history of life on Earth and I think the answer is yes. My main point is that they were small changes that compounded and they did not have to occur simultaneously in both sexes, although adaptations in each sex will be strongly influenced by adaptations in the opposite. [QUOTE][b]It seems that no matter what, a long string of mutations would have to occur, even for the simplest gender difference in a species.[/QUOTE][/b]I'm not convinced that a long series of mutations didn't occur to generate gender differences. Sexual polymorphisms simply do not exist in many lower forms of life that engage in sexual reproduction. Molds for example. Then you have organisms that have "male" and "female" parts that we can recognize but they're both on the same animal (snails for example) or on different parts of the animal or in different stages of the animal's development (some fish and some frogs can change sex with maturity or to meet environmental demands).I can speculate that gender differences began with specialized gametes. For example, paramecia exchange packages of DNA. A mutation in one paramecium might allow it to produce large quantities of these DNA packages (the gene coding for one of the major proteins involved might not switch off on queue). The adaptation would proliferate through the other paramecia but soon there would be too much competition in the population to play the game of spreading DNA effectively and producing all those packets would become a burden of energy and resources that didn't pay off as much as it originally did. Another member of the population suffer a mutation that switched off the protein permanently and it would use energy more efficiently than the others and have a bigger energy budget for asexual reproduction, proliferating itself through the population but with it and its daughter cells frequently acquiring DNA packets. The ratio of donors and acceptors would eventually reach equilibrium and since most of the population would be saturated with genes from other individuals (not all being expressed at once), mitosis of one "acceptor" could end up producing either a donor or an acceptor.This is, of course speculation. By the way we can take this scenario on a side-route and consider a packet that infects a cell and causes it to mass produce copies of that packet until the host cell dies. Then we have the evolution of a virus.

is they're any info on how those frogs are able to switch sexes?

​

[This message has been edited by KingPenguin, 02-06-2002]

quote:

---

Originally posted by Cobra_snake:
What I mean, is how many mutations would have to occur in both the male and female of the species to allow sexual reproduction. However, I'm sure you know of a simpler way in which sexuality could of occured without requiring these miracles (no sarcasticness intended on this comment). If you believe that sex could develop in a simpler way, could you please show me? It seems that no matter what, a long string of mutations would have to occur, even for the simplest gender difference in a species. Thanks.

---

You might be interested in the info. contained in
http://abcnews.go.com/sections/science/DailyNews/mutation990127.html
concerning the unexpectedly high rate of copying errors.Not exactly what you were looking for re: how to get from asexual to
sexual reproduction, but if cells can divide with four copy errors
per-division, and you have a 20-30 minute reproductive cycle ...
well that mounts up pretty fast.

If one is permitted to answer with DNA then I begin to ask what force torque makes that coded molecularly doubles a chemical equilbrium homogenously in a heterogenity that we confuse sex with the love needed to futher the idea without constraint as to the code calling.So an acridine that was became two sexes, else the G/C ratio is underinvestigation. But then why if not for replication of a double strand is there not more than a duo sexually?It exists.

Hi CobraFirstly there is a lot of work on the benefits of sexual reproduction. A good example I recall (but dont have a ref for sorry) was the repopulation of streams in Mexico when they are divided into pools by drought. The fish are represented by two reproductive modes- asexual females which only give rise to female offspring and male/female sexual reproduction. Ponds tend to get started with single individuals and asexual reproduction is the only mode available. Comparison of asexual ponds and sexual ponds revealed much higher rates of parasitism in the asexually reproducing fish- they couldnt out evolve the bugs in the ponds. Artificial introduction of male/female fish into asexual ponds saw the replacement of asexual reproduction with sexual.Secondly gender isnt as simple as male/female in some cases. In multicellular organisms it comes down to chromosomal compatibility and consequences of various combinations. Birds have W and Z chromosomes and it is the females are WZ and males are ZZ, unlike male mammals with XY and females with XX. There is a good accessable site I found talking about the weird world of sex:http://www.chaparraltree.com/...y-sex_and_reproduction.shtmlAs to info on gender swapping in frogs and fish- these organisms have no real primary sexual characteristics (ie no genitals for internal fertilisation). Their gametes are just produced in a big sack and expelled into the water. You couldnt do the same in a mammal because the genitals are products of embryogenesis. The difference between the development of an egg or a sperm is just a matter of turning on a different subset of genes during mitosis. The control of gender swapping is probably less well studied but seems to be influenced by the age and size of the organism or environmental conditions.Also in simple cases like paramecium I recall them being split into morpholgically indistinct sexual strains denoted by a + and - which preferentially mate with members of the other strain. I also recall that some protozoans only preferentially mate across sexual strains but can reproduce sexually with members of their own strain (hows that for "sexual preference"!!). This seems more like a case of one strain giving off a mating pheremone and the other having a receptor for it than their chromosomes differing markedly. The logistics of mating and the need for systems that allow organisms to find each other for sex is a good reason why gender would arise- it is a way of defining who has to chase who. Wouldnt it be impossible for an organism to use the same pheremone and receptor in one individual? How would it sort out the signal of others from its own? Any micro people capable of verifying this idea?So in short gender doesn't appear to have appeared suddenly, is flexible and adaptable and offers advantages for slowly reproducing organisms.Shane